I. Computer Networks
In a computer network, a group of computers and/or other devices communicate with each other via one or more communication links. One example of a network includes a pair of end stations each having a network interface, where the interfaces are connected to each other via a point-to-point network link. Another example of a network is shown in FIG. 1 and includes multiple computers 105A-0 each having one or more network interfaces. Each interface is connected to one or more other interfaces either directly or via one or more of switches 110A-D. For instance, as shown in FIG. 1, station 105A may be connected to station 105B via switch 110B, and station 105H may be connected to station 105I via a shared link to switch 110D. Yet another example of a network is the Internet, which is a network having many interconnected subnetworks.
Data to be transmitted, such as a file, is often divided into smaller units of data to be transmitted separately over one or more networks and re-assembled at a receiving computer. Each such unit of data is commonly called a “frame,” although it should be appreciated that data can be divided into frames in any suitable way, for example, according to any suitable communication protocol.
Any suitable communication link may be used to communicate data frames between network interfaces. For example, a link may be wired (e.g., electrical or optical) or wireless (e.g., radio, microwave, or infrared). A link may also be virtual (i.e., simulated).
Many network communication protocols have been developed over the years. A common model is the layered networking model, where communication functions are grouped into logical layers. For example, in an Open Systems Interconnection (OSI) model, there are seven layers arranged from top to bottom, each layer providing services to layers above and receiving services from layers below. For instance, Layer 2 (also known as the Data Link Layer) receives data transmission and reception services from Layer 1 (also known as the Physical Layer), and provides physical addressing services to Layer 3 (also known as the Network Layer).
Concepts of communications protocols layers, such as Layer 3 and Layer 2 of an OSI model, are explained in ITU-T (International Telecommunications Union—Telecommunications Standardization Sector) Recommendation X.200, “Information Technology—Open Systems Interconnection—Basic Reference Model: The Basic Model,” which is incorporated herein by reference.
II. Local Area Networks
In a local area network (also referred to as a LAN or local network), frames may be delivered after transiting the network with source and destination Layer 2 addresses, or interface source and destination addresses, associated with the frames unchanged or changed only to a form easily convertible to the original Layer 2 addresses. Examples of such local networks include, but are not limited to, bridged LANs and RBridged campuses.
It should be appreciated that local networks need not be “local” in a geographical sense. A local network may include components located in a geographical area of any suitable size (e.g., including multiple cities, states, and/or countries), and may even include components in outer space.
III. Virtual LANs
A local network may be subdivided into multiple overlaid logical networks called Virtual LANs or VLANs. A local network divided into VLANs may have the same physical structure as if not so divided. However, each data frame may, in some fashion, be labeled or categorized to indicate a VLAN to which the data frame belongs. Furthermore, a network interface may, in some fashion, be restricted or categorized in some suitable manner, so that switches may only send frames of certain labeling or categorization through interfaces with corresponding categorization. For example, certain network interfaces may be associated a particular type of traffic associated with a subset of VLANs, such as input traffic or output traffic, so that only that type of traffic associated with that subset of VLANs is sent through the interfaces.
In a local network supporting such VLANs, there may be end stations or switches that are unaware of VLANs and that receive and transmit unlabeled frames on one or more network interfaces of the end stations or switches. Such an unlabeled frame may be classified by an interface of the first VLAN-aware switch at which the frame arrives, to indicate a VLAN to which the frame belongs. The classification may be based on one or more values of one or more fields within the frame. Moreover, there may be VLAN-aware end stations that receive and transmit VLAN-labeled frames on one or more network interfaces, and/or classify unlabeled frames received on one or more interfaces as being in one or more specific VLANs.
A VLAN may include nested sub-VLANs and, likewise, may be enclosed by other higher-level VLANs. Thus, a “network” in the present disclosure may refer to any physical or virtual network, which may or may not include one or more subnetworks, and may or may not be included in one or more other networks as a subnetwork.